This invention has to do with automotive differentials of the type having a rotatable casing and a differential mechanism therein. More particularly, the invention is concerned with an anti-differential structure for use in a conventional automotive differential arrangement.
Automotive differentials are gear arrangements used to enable relatively different speeds of rotation by automotive axles and their wheels so that wheels driven by a common propeller shaft may travel different distances, as when a vehicle is turning a corner. Differentials for automobilies and like devices are well known as such.
It is in the nature of automotive differentials to respond to different rates of rotation of the vehicle wheels by a rolling accommodation which tends to distribute power differentially between the two wheels according to available traction.
It has long been recognized that this attribute of differential mechanisms is disadvantageous in certain circumstances. Most automobiles today can be obtained with anti-differential devices which serve to arrest or block the normal differential action for particular purposes. For example, when a vehicle has one wheel on a low traction surface such as ice or mud, an anti-differential mechanism will act to transmit power (which the differential normally would put at the less tractive wheel) toward both wheels, whereby the vehicle is able to remove itself from an icy or muddy area.
In automobile racing, the vehicles are not intended for street use, but anti-differential mechanisms are desirably provided for such vehicles in order that the action of the differential will deliver the tremendous power passed through the drive train to both wheels and not merely to the wheel having less traction, in this way improving racing performance.
Typical anti-differential devices available today use the phenomenon of the side gears (which are the gears coupled to the drive axles) moving laterally outward due to the involute pressure angle between the differential pinions and their side gears, to compress a friction material between the side gear axial faces and the wall surrounding the differential mechanism, that wall typically and hereinafter referred to as a casing. A differential casing is typically provided with opposed openings through which drive axles are passed and a third and possibly fourth opening through which shafts are inserted for the purpose of mounting the differential pinions. If rotation between the side gears and the differential casing is blocked, the differential action of the differential mechanism is likewise blocked and an anti-differential effect is obtained. The anti-differential effect alters the normal differential response and delivers power towards the axle which is driving its wheel in ice or mud, or in a drag racing situation, the right rear wheel which is otherwise sometimes lifted into the air so as to totally lose traction, and redistributes that power to both wheels including the wheel which has good traction.
As noted, the use of friction devices between the side gears and the casing has been proposed and adapted in many instances to obtain an anti-differential effect. Known friction discs have not always proven satisfactory in heavy duty anti-differential situations, particularly drag racing. The binding effect obtained between the casing and the side gear, particularly in repetitive applications, and moreover the release characteristics of known anti-differential structures, have been found wanting, in that such structures can hang up and load the drive train unnecessarily, as well as diminish the driver's control of his vehicle. These latter effects are highly dangerous in various racing situations.